Switch method for switching class amplifiers

ABSTRACT

In accordance with one the present disclosure, systems and methods are disclosed that include transmitting a binary signal from a signal source into a switch where the switch is in series between the signal source and a first circuit element. In addition, the switch is operating substantially in a switched mode and creates a switched output signal and the switch is controlled by the binary signal. Also disclosed in this method is detecting a negative voltage in a signal from a second circuit element. In this method the first circuit element is in series between the second circuit element and the switch, and upon detecting the negative voltage from the second circuit element the first circuit element creates high impedance in the first circuit element.

TECHNICAL FIELD

The present disclosure relates to amplifiers and in particular tomethods of operating switching class amplifiers.

BACKGROUND

Power amplifiers of the Class-A and Class-AB type have been employed asradio frequency (RF) power amplifiers for cellular base station andother RF systems. These amplifiers are based on the operation of atransistor primarily in its linear mode and are used in audio or otherlower frequency operations. One problem with operation in linear mode istheir limited ability to efficiently amplify RF signals.

In order to overcome this limitation, a new class of switchingamplifiers has been developed. These amplifiers use transistorsoperating in a highly nonlinear mode, referred to as switch mode. Theoperation of transistors in the switched mode results in amplifiers witha higher efficiency than those that operate in a linear mode.

Switching mode amplifiers have seen many years of use in variouselectronic systems including audio and RF power amplifiers and switchingpower supply circuits. One example of a switching mode amplifier is aClass-D amplifier. Other examples of switching class amplifiers include,but are not limited to E, F, and S class amplifiers.

The Class-D amplifier architecture may be used in a plurality ofapplications. However, these amplifiers suffer from a number ofproblems, including device parasitics such as drain-source capacitanceand lead inductance that result in high loss of power in each cycle.

SUMMARY

In accordance with one embodiment, a method is disclosed that includestransmitting a binary signal from a signal source into a switch wherethe switch is in series between the signal source and a first circuitelement. In addition, the switch is operating substantially in aswitched mode and creates a switched output signal and the switch iscontrolled by the binary signal. Also disclosed in this method isdetecting a negative voltage in a signal from a second circuit element.In this method the first circuit element is in series between the secondcircuit element and the switch, and upon detecting the negative voltagefrom the second circuit element the first circuit element creates highimpedance in the first circuit element.

In accordance with another embodiment, a system is disclosed thatincludes a binary signal source and a switch coupled to the binarysignal source that is controlled by the binary signal source. Also inthis embodiment, a first voltage controlling element is disclosed thatis coupled to the switch and a transformer. In this embodiment, thefirst voltage controlling element creates a high impedance state withinthe first voltage element in response to a negative signal from a secondsource.

In yet another embodiment, a system is disclosed that includes atransformer that propagates a signal. Also in this embodiment is atransistor that is coupled to the transistor and is operated in aswitched mode. The transistor is controlled by a binary data source.Also in this embodiment is a signal blocker that is placed in series inbetween the transformer and the transistor that creates a high impedancestate upon detecting a negative signal from the transformer.

Other technical features may be readily apparent to one skilled in theart from the following figures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, wherein likenumbers designate like objects, and in which:

FIG. 1 depicts a high level diagram of an example system using anenhanced amplifier, in accordance with the present disclosure;

FIG. 2 is a block diagram of an example embodiment of a system using anenhanced amplifier, in accordance with the present disclosure;

FIG. 3 is another block diagram of an example embodiment of a systemusing an enhanced amplifier, in accordance with the present disclosure;

FIG. 4 is a flowchart of one method of operating an enhanced amplifier,in accordance with the present disclosure; and

FIG. 5 is a block diagram of a communications device using an enhancedamplifier, in accordance with the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates an example system 4 using an enhanced amplifier 10.In this example embodiment, a signal source 6 transmits a binary digitalsignal into an enhanced amplifier 10. The enhanced amplifier 10 acceptsthe signal from the signal source 6 and transmits an amplified signalinto an output device 8. The signal from the enhanced amplifier 10 maybe conditioned or filtered prior to being input to the output device 8.Enhanced amplifier 10 includes a plurality of components for enhancingthe efficiency of the enhanced amplifier 10.

During operation of system 4 using a non-enhanced amplifier, if thesignal source 6 is a waveform that contains switching events that arenot harmonically related to the natural frequency of the non-enhancedamplifier, the non-enhanced amplifier may experience significantnegative voltages across the drain source channels of the transistorswithin the non-enhanced amplifier. These negative voltages can createbias conditions for the non-enhanced amplifier resulting in an undesiredconduction path that interferes with proper operation of thenon-enhanced amplifier.

Utilizations of the enhanced amplifier 10 having an element, such as aforward biased diode, that effectively presents high impedance in serieswith an open switch and low impedance in series with a closed switchwithin the amplifier, allows for operation of the enhanced amplifier 10without being adversely affected by the negative voltages. Therefore,the enhanced amplifier 10 is more efficient than the non-enhancedamplifier.

FIG. 2 is a diagram of one example embodiment of enhanced amplifier 10.In this embodiment, a choke 12 is coupled to a voltage source (notshown) and a first switch unit 26 and a second switch unit 28. A firstside of a transformer 14 is coupled to the first switch unit 26 and thesecond switch unit 28, while a second side is connected to a filter 16and ground.

Signal source 6 is coupled to the first switch unit 26 and the secondswitch unit 28. Signal source 6 transmits a binary digital signal usedas a control signal into the first switch unit 26 and the second switchunit 28. A filter 16 is coupled to a load 18.

When a supply voltage signal is applied to the choke 12, the choke 12provides a DC bias current Idd to the first switch unit 26 and thesecond switch unit 28. Each switch, when closed, receives a signal equalto the bias current Idd resulting in the effective switching of the biascurrent Idd alternately between switch 26 and switch 28. As shown inFIG. 2, the outputs of the first switch unit 26 and the second switchunit 28 are coupled together through the transformer 14.

By opening and closing the switches 26 and 28 in a complementary,alternating fashion, the currents supplied by the choke 12 are convertedinto an output signal by the transformer 14. The output signal istransmitted through the filter 16 and then delivered to the load 18.However, there may be errors in the switching process. In such a case,the first switch unit 26 and the second switch unit 28 may be exposed toa negative signal. These signals can cause damage to the first switchunit 26 and the second switch unit 28. Enhanced amplifier 10 overcomesthese problems through additional circuit elements. One of each of theseadditional circuit elements is placed in series between the switch unit26 and rest of the circuit, for example, the transformer 14 and thechoke 12. Another additional circuit element is placed in series betweenthe switch unit 28 and rest of the circuit, for example, the transformer14 and the choke 12.

Since the signals created by the first switch unit 26 and the secondswitch unit 28 may not be directly inverses of each other, a two-sidedsignal may be created. The phrase “two-sided signal” relates to a signalwith two main components, consisting of a first signal that is createdon one side of the amplifier (e.g., first switch unit 26) and anothersignal that is created on the other side of the amplifier (e.g., secondswitch unit 28). In general, these signals are not direct inverses ofeach other as in a differential circuit, and are generally time shiftedfrom each other and ideally non-overlapping in time and are ideallyalways positive relative to the negative supply voltage. A two-sidedsignal may also damage the first switch unit 26 and the second switchunit 28.

The first switch unit 26 and the second switch unit 28 comprise circuitelements that allow current flowing in the choke 12 to be directed tothe first switch unit 26 or the second switch 28. For example, if thefirst switch unit 26 is closed, it presents a low impedance path toground for current in the choke 12. At the same time, the switch 28 willbe open, presenting a high impedance path to ground. This directs thecurrent to flow to the first switch unit 26. The operation of the firstswitch unit 26 may be substantially similar to the second switch unit28.

The output signal is also transmitted into the filter 16. The filter 16removes undesired frequencies from the signal. The filter 16 isconnected to the load 18 and the ground 20.

It is understood that the enhanced amplifier 10 may use any kind oftransistor. Examples of transistors that may be used in the first switchunit 26 and the second switch unit 28 include, but are not limited to,field-effect transistor (FET), bipolar junction transistor (BJT), andPseudomorphic High Electron Mobility Transistors (PHEMT). It is furtherunderstood that during the normal operation of the transistor, anegative voltage may be introduced onto the drain or collector of thetransistor or be created by the transistor. Therefore, not only does theenhanced amplifier 10 compensate for negative voltages from atransformer, but also from other external sources (e.g., other inputsinto the transistor) as well as internal sources (e.g., transistoroperation).

The choke 12 may, in some embodiments, be an inductor that has a largeinductance value. The choke 12 may have a low DC resistance and veryhigh AC/RF impedance. It is understood that the choke 12 may supply DCcurrent to the circuit with low levels of AC/RF current. In otherembodiments, choke 12 could be replaced with a DC current source.

The transformer 14 is configured to take the difference between thecomponents of a two sided signal to create a composite signal. Signalscoming into the transformer 14 ideally have substantially positivecomponent relative to the negative voltage supply. When those signalsleave the transformer 14, they will have a positive and a negativecomponent relative to ground. The effect of the transformer 14 is tosubtract the signals present at nodes X and Y (where X is the nodebetween the switch 26 and the transformer 14 and Y is the node betweenthe switch 28 and the transformer 14 in FIG. 2).

The first switch unit 26 comprises at least one-transistor capable ofoperating in a saturated or switched mode and one voltage-controllingelement. One example of the voltage-controlling element is a diode. Inthe operation of the switching element, there exists the possibilitythat the voltage across the first switch unit 26 may become negative.The negative signal may be from any source, including the transformer14. In such an event, the first switch unit 26 may become damaged orturned on upside down. When the transistor is “turned on upside down” ithas effective impedance that is low when it should be high. Thiscondition interferes with the proper operation of the circuit andintroduces high inefficiencies. Through the use of a voltage-controllingelement in series with the switch, when the voltage entering the firstswitch unit 26 becomes negative, the voltage-controlling element willturn off and present high impedance in series with the switch. Thisallows for the proper operation of the first switch unit 26 and mayimprove the efficiency of the first switch unit 26. It is understoodthat there may be slight power dissipation because of thevoltage-controlling element. This power dissipation may be taken intoaccount when designing the enhanced amplifier 10.

It is explicitly understood that while the example illustrated in FIG. 2allows for a positive signal to be used by the first switch unit 26, itis possible to configure the enhanced amplifier 10 to only use negativerather than positive signals. The configuration of enhanced amplifier 10may, in some embodiments, only require that a consistent state ofoperation (e.g., positive or negative) be used during the operation ofthe enhanced amplifier 10.

The ground 20, as with other grounds used throughout this disclosure,may relate to either a termination point of a signal, or a point atwhich the signal leaves the enhanced amplifier 10. The use of the term“ground” is only intended to infer that the signal within the enhancedamplifier 10 is being transmitted out of the enhanced amplifier 10. Twoexamples of this transmission are placing the signal to a ground stateor transmitting the signal to another circuit element outside of theenhanced amplifier 10.

FIG. 3 is a diagram of one example embodiment of the enhanced amplifier10 and is substantially similar to the embodiment shown in FIG. 2. InFIG. 3, the first switch unit 26 has been replaced with a first diode 44and a first transistor 40. In addition in FIG. 3, the second switch unit28 has been replaced with second diode 46 and second transistor 42.Signal source 6 has been coupled to first transistor 40 and secondtransistor 42.

In the embodiment of FIG. 3, the series configuration of the first diode44 and first transistor 40 is shown. In addition, the seriesconfiguration of the second diode 46 and the second transistor 42 isshown. In the event that the voltage at the anode of the added diodebecomes negative, the diode in FIG. 3 will act as thevoltage-controlling element described in FIG. 2.

FIG. 4 is a flowchart 90 of one embodiment of the present disclosure. Inblock 92, a signal is transmitted from a switch source into a circuitelement, where the circuit element is in series between the output and aswitch. In block 94, a negative voltage is detected in the outputsignal, and upon detecting the negative voltage the circuit elementcreates high impedance in series with the switch and the output. Inblock 96, a positive voltage is detected in the signal, and upondetecting a positive voltage creating a low impedance path through thecircuit element.

As shown in FIG. 5, enhanced amplifier 10 may be incorporated into acommunications device 190. The exemplary communications device 190 is amedium to high-power multi-channel, two-way radio in a fixed location.Typically low-power, single-channel, two-way radios or wireless devicessuch as mobile phones, portable phones and wireless routers may use it.The communications device 190 may comprise a signal controller 200 thatis coupled to a transmitter 202 and a receiver 204. Transmitter 202 andreceiver 204 (or combined transceiver) are further coupled to an antenna206. In the communications device 190, digital signals are processed ina channel processing circuitry. The digital signals may be signals for awireless communication system, such as signals that convey voice or dataintended for a mobile terminal (not shown). The communications device190 may employ any suitable wireless technologies or standards such as2G, 2.5G, 3G, GSM, IMT-2000, UMTS, iDEN, GPRS, 1xEV-DO, EDGE, DECT, PDC,TDMA, FDMA, CDMA, W-CDMA, LTE, TD-CDMA, TD-SCDMA, GMSK, OFDM, WiMAX, thefamily of IEEE §802.11 standards, the family of IEEE §802.16 standards,IEEE §802.20, etc. Signal controller 200 then transmits the digitalsignals to transmitter 202. A radio frequency (RF) generator 210modulates the signals onto an RF signal. RF generator 210 may comprisethe enhanced amplifier 10. The resulting output signal is transmittedover antenna 206 to the mobile terminal. Antenna 206 also receivessignals sent to base station 190 from the mobile terminal. Antenna 206couples the signal to receiver 204 that demodulates them into digitalsignals and transmits them to signal controller 200 where they may berelayed to an external network 212. Base station 190 may also compriseauxiliary equipment such as cooling fans or air exchangers for theremoval of heat from the communications device 190.

In an embodiment, one or more embodiments of the enhanced amplifier 10may be incorporated into the communications device 190 in lieu of parts,if not all, of RF generator 210, which may decrease the capital costsand power usage of the communications device 190. The power amplifierefficiency measures the usable output signal power relative to the totalpower input. The power not used to create an output signal is typicallydissipated as heat. In large systems such as the communications device190, the heat generated in may require cooling fans and other associatedcooling equipment that may increase the cost of the communicationsdevice 190, require additional power, increase the overall size of thebase station housing, and require frequent maintenance. Increasing theefficiency of the communications device 190 may eliminate the need forsome or all of the cooling equipment. Further, the supply power toenhanced amplifier 10 may be reduced since it may more efficiently beconverted to a usable signal. The physical size of the communicationsdevice 190 and the maintenance requirements may also be reduced due tothe reduction of cooling equipment. This may enable the communicationsdevice 190 equipment to be moved to the top of a base station tower,allowing for shorter transmitter cable runs and reduced costs. In anembodiment, the communications device 190 has an operating frequencyranging from about 450 MHz to about 3.5 GHz.

It may be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation. The term “or” is inclusive, meaning and/or. The phrases“associated with” and “associated therewith,” as well as derivativesthereof, mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like.

While this disclosure has described certain embodiments and generallyassociated methods, alterations and permutations of these embodimentsand methods will be apparent to those skilled in the art. Accordingly,the above description of example embodiments does not define orconstrain this disclosure. Other changes, substitutions, and alterationsare also possible without departing from the spirit and scope of thisdisclosure, as defined by the following claims.

1. A method, comprising: transmitting a binary signal from a signalsource into a first switch and a second switch, wherein the first switchis in series between the signal source and a first circuit element, andthe second switch is in series between the signal source and a secondcircuit element, and wherein the first switch and second switch generatea first and second switched output signal, wherein the first and secondswitches are operated in an alternatively complementary fashion; anddetecting a negative voltage in a signal from a signal transformingelement, and upon detecting the negative voltage from the signaltransforming element the first circuit element creates a high impendancein the circuit element.
 2. The method of claim 1, wherein the binarysource is a sigma-delta modulation (SDM) source.
 3. The method of claim1, wherein the first circuit element is a diode.
 4. The method of claim1, wherein the second circuit element is a transistor.
 5. The method ofclaim 1, wherein the switch is a transistor.
 6. The method of claim 4,wherein the transistor is selected from a group comprising: field-effecttransistor (FET), bipolar junction transistor (BJT), and PseudomorphicHigh Electron Mobility Transistors (PHEMT).
 7. The method of claim 5,wherein the signal transforming element is a transformer, wherein thetransformer senses the switched output signal during periods when thefirst circuit element does not create a high impedance state in thefirst circuit element, and wherein the transformer adjusts analternating current signal based upon the output switched signal, andwherein the transformer outputs a direct current signal.
 8. The methodof claim 7, wherein the first circuit element is a transistor.
 9. Themethod of claim 1, wherein the switch is part of a switching classamplifier.
 10. A system, comprising: a binary signal source; a first andsecond switch coupled to the binary signal source, wherein the first andsecond switch are controlled by the binary signal source, and whereinthe first switch and second switch operate in an alternativelycomplementary fashion; a first voltage controlling element, wherein thevoltage controlling element is coupled to the first switch and atransformer; a second voltage controlling element, wherein the secondvoltage controlling element is coupled to the second switch and thetransformer; and wherein the first voltage controlling element creates ahigh impedance state within the first voltage element in response to anegative signal.
 11. The system of claim 10 wherein the switch is atransistor.
 12. The system of claim 11, wherein transistor is selectedfrom a group comprising: field-effect transistor (FET), bipolar junctiontransistor (BJT), and Pseudomorphic High Electron Mobility Transistors(PHEMT).
 13. The system of claim 10 where the voltage controlling unitis a diode.
 14. The system of claim 10, where signal source is adelta-sigma modulation (SDM) source.
 15. A system, comprising: atransformer, wherein the transformer propagates a signal; a firsttransistor, wherein the first transistor is coupled to the transformerthrough a first signal blocker, wherein the transistor is controlled bya binary data source; and a second transistor, wherein the secondtransistor is coupled to the transformer through a second signalblocker, wherein the second transistor is controlled by the binary datasource, and wherein the first and second transistor are operated in analternatively complementary fashion and the first and second signalblocker create a high impedance state upon detecting a negative signal.16. The system of claim 15, wherein the transistor creates an outputsignal.
 17. The system of claim 15 wherein the transformer propagatesboth positive and negative signals, and wherein the signal blocker is adiode and blocks negative signals created by the transformer.
 18. Thesystem of claim 15, wherein the signal blocker is a device that switchesfrom a state of high resistance to low resistance.
 19. The system ofclaim 15, wherein the transistor is a device that switches from a stateof high current to a state of low current.
 20. The system of claim 15,wherein the transistor is a switching class amplifier.